The examples in the reference https://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.linalg.expm_multiply.html clearly understand that both NDArray and sparse matrices are valid linear operators. However, the current type hints https://github.com/scipy/scipy-stubs/blob/master/scipy-stubs/sparse/linalg/_expm_multiply.pyi only contemplate objects of type LinearOperator, which does not include the former.